Process for Denitration of Exhaust Gas

Abstract

A denitration process for removing nitrogen oxides contained in low-temperature exhaust gas at a high denitration rate; namely, a denitration process for reductively removing nitrogen oxides contained in an exhaust gas (x) containing nitrogen monoxide and sulfur dioxide. The process comprises a preliminary step 2 of partially oxidizing nitrogen monoxide in the exhaust gas to form nitrogen dioxide, a radical formation step 3 of adding a nitrogen compound and a hydrocarbon compound to a high-temperature zone 22 to form amine radicals (r), and a denitration step 4 of mixing the amine radicals (r) with the pretreated gas (p) containing nitrogen monoxide and nitrogen dioxide that was discharged from the preliminary step 2. As a result, nitrogen oxides in the exhaust gas (x) are reductively decomposed.

Description

TECHNICAL FIELD[0001]The present invention relates to a process for the denitration of exhaust gas, and more specifically, to a process for the denitration of exhaust gas wherein nitrogen oxides are reductively removed from exhaust gas exhausted from an engine such as a diesel engine for a ship or power generator.BACKGROUND ART[0002]In recent years, much attention has been focused on the reduction of particulate matter and nitrogen oxides exhausted from automotive diesel engines such as those on buses and trucks. Similarly, the removal of harmful substances contained in the exhaust gas of engines such as diesel engines for ships and power generators, boiler exhaust gas, and plant off-gas is an important problem. However, while automotive diesel engines use diesel fuel oil for fuel, which has a low sulfur content, diesel engines such as those on ships and power generators use high sulfur content fuel known as Class A or Class C fuel oils (JIS standard). For this reason, the exhaust g...

AI Technical Summary

Benefits of technology

[0067]In the present invention, the gas subjected to treatment is not particularly limited, and may for example include exhaust gas from a diesel engine on a ship or power generator, exhaust gas from an automotive diesel engine, boiler exhaust gas, or plant off-gas. Typically, exhaust gas from diesel engines contains harmful substances such as particulate matter, nitrogen oxides, and sulfur oxides. In many cases, particulate matter is present primarily as soot, nitrogen oxides are present primarily as nitrogen monoxide, and sulfur oxides are present primarily as sulfur dioxide. The concentration of sulfur oxides in the exhaust gas (x) is preferably 50 ppm or greater, more preferably 100 ppm or greater, and preferably 500 ppm or greater in particular. In this concentration range, the effectiveness of the invention becomes more pronounced.

[0068]Moreover, as the temperature of the exhaust gases from diesel engines on ships and power generators are comparatively low, conventionally they have been difficult to apply non-catalytic denitration processes to the gases as-is. However, the denitration process of the present invention, an object thereof being to raise the denitration efficiency of such exhaust gas, is able to treat such exhaust gas as-is without heating or warming treatments. Not only that, denitration can be performed with a high efficiency. The temperature of the exhaust gas is preferably 200° C. to 450° C., more preferably 250° C. to 450° C., and preferably 250° C. to 300° C. in particular. Even at such low temperatures, sufficient denitration effects are obtainable.

[0069]The diesel engine fuel is not particularly limited, and light oil, Class A heavy fuel oil, Class C heavy fuel oil, DME or similar oil may be used. Among these, it is preferable to use a fuel that contains a sulfur component in order to make use of the characteristics of the denitration process of the invention, and thus Class A heavy fuel oil and Class C heavy fuel oil are preferable. Class A heavy fuel oil is stipulated by JIS standard (JIS K2205) as having a sulfur content of not more than 0.5 mass % for Category 1 No. 1 fuel, and not more than 2.0 mass % for Category 1 No. 2 fuel, while Class C heavy fuel oil is stipulated as having a sulfur content of not more than 3.5 mass % for Category 3 No. 1 fuel. Among these, the Class A heavy fuel oil used in diesel engines such as those on ships and diesel power generators primarily has a sulfur content of not more than 0.2 mass %, while the Class C heavy fuel oil primarily has a sulfur content of not more than 3.5 mass %.

[0070]Hereinafter, the present invention will be described in further detail by describing embodiments thereof. However, it should be appreciated that the scope of the invention is not to be limited to these embodiments.EMBODIMENTS

[0071]Using the test equipment shown in FIG. 5, exhaust gas was treated for denitration, and the concentration of nitrogen oxides as well as the concentration of sulfur oxides were measured for each step.

[0072]In FIG. 5, exhaust gas from a diesel engine 1 is drawn into a flue 10 and a bypass line 7, wherein the preliminary step 2 and denitration steps 4 are disposed in the flue 10, and radical formation steps 3 are disposed to communicate to the denitration steps 4. The high-temperature zones of the radical formation steps 3 are formed at the downstream tips of burner flames. The sizes of the piping used and the gas flow rate in the pipes were those shown in Table 1.TABLE 1Piping innerGas flowdiameter (mm)rate (mN / s)Flue 101501Pipe portion 51003Nitrogen compound nozzle 848Hydrocarbon compound 948

Problems solved by technology

Similarly, the removal of harmful substances contained in the exhaust gas of engines such as diesel engines for ships and power generators, boiler exhaust gas, and plant off-gas is an important problem.

For this reason, the exhaust gas of the latter contains a large amount of sulfur oxides, and processing the gas to remove harmful substances is a significant obstacle.

50° C. to 450° C.) exhaust gas exhausted from diesel engines such as those on ships and power generators, it is necessary to pre-treat the exhaust gas to heat it and raise the temperature thereof, which in turn leads to increased treatment costs and makes the application of non-catalytic denitration problematic.

In addition, while non-catalytic denitration using ammonia achieves a high denitration rate at the laboratory level, it has been difficult to obtain a denitration rate exceeding 50% in an actual furnace such as a boiler.

However, the denitration rate of this process is only approximately 40% under equimolar conditions of nitrogen oxides and ammonia.

Furthermore, if ammonia is excessively supplied in order to raise the denitration rate, unreacted ammonia remains and treatment costs increase.

Moreover, in the case where the exhaust gas contains sulfur oxides, ammonium sulfate is created, so that the treatment thereof leads to worsened cost-effectiveness.

However, this SCR process is inferior to the non-catalytic denitration process in that it uses a large quantity of SCR catalyst.

Furthermore, there is the problem that when the exhaust gas temperature is 300° C. or less, sulfur dioxide in the exhaust gas that has oxidized to sulfur trioxide and the like reacts with the ammonia to create ammonium hydrogen sulfate, which poisons the SCR catalyst and reduces catalytic activity.

However, the denitration rate in this denitration process is not entirely sufficient, and there is demand to further raise the denitration rate.Patent Literature 1: U.S. Pat. No. 6,066,303Patent Literature 2: Japanese patent application Kokai publication No. 2002-136837Patent Literature 3: Japanese patent application Tokuhyo publication No. 2001-525902Patent Literature 4: Japanese patent application Kokai publication No. 2005-254093Non-patent Literature 1: “Fuel Conversion and SOX / NOX Countermeasure Technologies: A Focus on Exhaust Desulfurization / Denitration”, by Junpei Ando (Project News, Jun. 25, 1983, p.

Images